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Model 3 Battery Details

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As I understand it, instead of heating the battery directly, they are going to heat up the motor first, and then use heat from the motor to warm the battery. So it will be slower to warm up the battery and be less efficient.

So lower cost but also worse performance.

That's not really the right way of looking at it. The motor is acting as a resistive heater in exactly the same way as a dedicated resistive heater. In both cases they heat fluid that runs through the battery to heat the cells. The dedicated resistive heater doesn't heat the battery any more directly than this method, and the only way it would be slower is if the motor is able to use less power to do resistive heating, which we don't know.
 
According to Electrek, car uses electric motor to create heat and warm up the battery. But I can't see what is the rationale, as weight and cost savings must be minimal.

Tesla, like SpaceX, uses literally every trick in the book for cost reduction. Actually all car manufacturers seem to do this - the stories of $3 car part savings are legendary.
 
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I can think of one advantage of this, over just the cost savings: they won't be limited to just 6kW.

As for the comment "wouldn't that cool the motor", re: the heat flow diagram: if you're running the compressor at the same time you're trying to heat up the cabin and battery pack, sure. But why would you be trying to heat and cool simultaneously?
 
None of us knows if the new method is better or worse than the one used on S and X.
But what exactly in Tesla's culture and history leads you to believe they will move to a less efficient heating method for the pack?
Remember Elon said on the last CC that they have money set aside to bring all models up to the current tech level.
I take that statement as bringing S and X up to the current Model 3 tech. Model 3 may be cheaper than S and X but the tech is always evolving.
There is a reason for example the Semi revealed next month uses Model 3 motors and not Model S motors.

Battery cooling isn't self driving...

Why would they go for less efficient heating? Because it's cheaper probably. They don't even have a heat pump on the S/X so they don't care too much anyways.
 
That's not really the right way of looking at it. The motor is acting as a resistive heater in exactly the same way as a dedicated resistive heater. In both cases they heat fluid that runs through the battery to heat the cells. The dedicated resistive heater doesn't heat the battery any more directly than this method, and the only way it would be slower is if the motor is able to use less power to do resistive heating, which we don't know.

But in one care you also heat up the whole motor, which then dissipates heat everywhere, not only the cooling jacket.
 
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As I understand it, instead of heating the battery directly, they are going to heat up the motor first, and then use heat from the motor to warm the battery. So it will be slower to warm up the battery and be less efficient.

So lower cost but also worse performance.

That's not really the right way of looking at it. The motor is acting as a resistive heater in exactly the same way as a dedicated resistive heater. In both cases they heat fluid that runs through the battery to heat the cells. The dedicated resistive heater doesn't heat the battery any more directly than this method, and the only way it would be slower is if the motor is able to use less power to do resistive heating, which we don't know.

Nuh-uh! YOU'RE the one who's looking at it wrong! :p ;) J/k.

Seriously tho... a motor has a lot of mass and thermal inertia or heat capacity. (I.e., it has a lot of metal that will take significant amounts of energy to heat up.) A dedicated resistive heater, in contrast, has very little mass and thermal inertial and will heat up very quickly without using a lot of energy. Therefore almost all of the energy will go to heating the coolant and not heating the heater itself.

Then there's also probably an issue with temperature differentials. Heat transfer rates are proportional to the difference in temperature. A resistive heater that gets very hot, so it performs well. But, presumably, the motor would not be able to get nearly as hot, and therefore it's performance as a heater would be more limited.

Also, presumably the motor would lose some heat to any mating components... gears, mounts, etc.

So... slower and less efficient.

(I shouldn't have originally said that a dedicated battery heater "directly" heats the battery. It heats coolant which then heats the battery.)
 
Nuh-uh! YOU'RE the one who's looking at it wrong! :p ;) J/k.

Seriously tho... a motor has a lot of mass and thermal inertia or heat capacity. (I.e., it has a lot of metal that will take significant amounts of energy to heat up.) A dedicated resistive heater, in contrast, has very little mass and thermal inertial and will heat up very quickly without using a lot of energy. Therefore almost all of the energy will go to heating the coolant and not heating the heater itself.

Then there's also probably an issue with temperature differentials. Heat transfer rates are proportional to the difference in temperature. A resistive heater that gets very hot, so it performs well. But, presumably, the motor would not be able to get nearly as hot, and therefore it's performance as a heater would be more limited.

Also, presumably the motor would lose some heat to any mating components... gears, mounts, etc.

So... slower and less efficient.

(I shouldn't have originally said that a dedicated battery heater "directly" heats the battery. It heats coolant which then heats the battery.)

The motor is going to heat up anyway, unless you are planning to sit in your car twiddling your thumbs. I can except that it might be slower, but I don't believe it will be less efficient.
 
Less efficient heating ... because electric energy will go ... eh where exactly?
Every and all electric heaters, what ever they look like, are 100% efficient.
Except of those old light bulbs that only turned some 99% of energy into heat, about 1% was lost as light.
As long as the motor wont turn red hot, it will be 100% efficient heating element.

Sweet Jesus ...
 
According to Electrek, car uses electric motor to create heat and warm up the battery. But I can't see what is the rationale, as weight and cost savings must be minimal.
It's a brilliant idea. As well is the cost of the heater, they have eliminated the cost of connectors, control module, installation time, and even more importantly there are several less potential points of failure.
 
You do save by not having to haul the extra weight of the heater all the time, even when not in use. So even if the power train method of heating is less efficient, you would get longer range when it’s warm

You also gain by reduced number of components to service/maintain. We've had a battery heater core fail in our early 2013 Model S, so Tesla may have done an analysis of failure rates and chosen to heat using a system that was more robust or cheaper to produce and maintain.
 
a motor has a lot of mass and thermal inertia or heat capacity. (I.e., it has a lot of metal that will take significant amounts of energy to heat up.) A dedicated resistive heater, in contrast, has very little mass and thermal inertial and will heat up very quickly without using a lot of energy. Therefore almost all of the energy will go to heating the coolant and not heating the heater itself.
This is exactly what I was thinking. Given my location I have a strong interest in this topic.. plan to preheat in the morning but by 10 hrs later in below 0F that could be some serious preheating necessary (via app). Given the thermal mass of the motor, I wonder what the breakeven of just keeping it warm would be.. or is that a waste regardless?

I really don't want to wait for the cabin to heat up or components of the car (like regen) to begin working 15+ mins after I get in the vehicle, even if I waste battery / range (since I don't expect to get close to the range limits for commuting).
 
I really don't want to wait for the cabin to heat up or components of the car (like regen) to begin working 15+ mins after I get in the vehicle, even if I waste battery / range (since I don't expect to get close to the range limits for commuting).

I think cabin heating is completely separate from the drivetrain heating. (Just like on the Model S/X.)

I saw that from the information on the Electrek article:
Tesla Model 3 Electronics.png

1. Charge port connector 2. Fast charge contactor assembly 3. Coolant line to PCS 4. PCS – Power Conversion System 5. HVC – High Voltage Controller 6. Low voltage connector to HVC from the vehicle 7. 12V output from PCS 8. Positive HV power switch 9. Coolant line to PCS 10. HV connector to cabin heater and compressor 11. Cabin heater, compressor and PCS DC output fuse 12. HV connector to rear drive unit 13. HV pyro fuse 15. HV connector to front drive unit 16. Negative HV power switch 17. Connector for 3 phase AC charging

It shows that the cabin heater gets its power directly from the electronic module in the Model 3 battery pack, which means there is still an electric cabin heater. (In the Model S/X that have a physically separate DC-DC converter that powers the cabin heater and compressor.)

What we don't know is will setting the car to pre-heat the cabin also trigger the battery to get preheated so that regen can be full strength immediately?
 
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I'm not sure why people are thinking this would somehow be slower. On MS/MX you're limited to two 6kW heaters But the motor, running at full power and 0% efficiency would be in the low hundreds of kW. Now I'm sure that they can't actually run it that hot at 0% efficiency, I'm sure they can't remove heat that fast, but the key is, it's not going to have any trouble kicking out heat - and fast.